1. Field of the Invention
The present invention relates to a throttle positioner and, more particularly, an improvement thereof with regard to its performance.
2. Description of the Prior Art
When an automobile is decelerated while it is running, the amount of uncombusted components in the exhaust gas significantly increases. In order to solve this problem, a device which is called a throttle positioner has been proposed. The throttle positioner operates to hold a throttle valve at a predetermined opening position where it is slightly opened from an idling position when an automobile is decelerated, thereby maintaining a predetermined minimum amount of air supply through an intake tube, thus avoiding heavy emission of uncombusted material in the exhaust gas.
Conventionally, the throttle positioner comprises a port to detect intake vacuum, a diaphragm means, a conduit means which connects said port and said diaphragm means, said conduit means including a means to delay transmission of vacuum, a throttle positioning lever adapted to be driven by said diaphragm means so as to rotate between first and second rotary positions, and a throttle driving lever mounted on a rotary shaft of a throttle valve and adapted to engage a tip of said throttle positioning lever so as to hold return of the throttle valve at a predetermined opening position when said throttle positioning lever is in said first rotary position while disengaging from said tip of said throttle positioning lever so as to allow for full return of the throttle valve to an idling position when said throttle positioning lever is in said second rotary position. In a throttle positioner of the aforementioned kind, when an automobile is running at a constant speed or being accelerated with the throttle valve being turned to a relatively large opening position, the intake vacuum detected by said port is relatively low (small) and, accordingly, the diaphragm is loosened in one direction thereby turning said throttle positioning lever to said first rotary position. If, in this condition, the accelerating pedal is released to decelerate the automobile, thereby rotating the throttle valve toward its closing position, said throttle driving lever mounted to the rotary shaft of the throttle valve engages said tip of the throttle positioning lever, whereby the throttle valve is checked from returning to its idling position and is maintained at a throttle opening position where the throttle valve is slightly opened from the idling position. When the throttle valve has been closed to said throttle opening position, the intake vacuum detected by said port rapidly increases up to a relatively large value. The increased intake vacuum is transmitted to the diaphragm chamber of the diaphragm means through said means to delay transmission of vacuum with a predetermined time delay effected by said delay means. Then, as the intake vacuum applied to the diaphragm chamber gradually increases, the diaphragm means is tightened in a direction opposite to the aforementioned loosening direction, thereby correspondingly turning the throttle positioning lever toward said second rotary position. After the lapse of a predetermined time from the beginning of deceleration, said time being adjusted by said means to delay transmission of vacuum, the throttle positioning lever reaches said second rotary position and the tip of the throttle positioning lever disengages from the throttle driving lever, whereby the throttle valve is released from the restriction applied by the throttle positioning lever and is permitted to return to its idling opening position.
Now, in the case of a modern autombile which is equipped with an oxidizing catalytic converter in its gas exhausting system for the purpose of purifying exhaust gases, there is a problem in that if the throttle positioner is released after a relatively short lapse of time, thereby turning the throttle valve to its idling position when the automobile is running on a relatively long downhill slope, a relatively large amount of uncombusted components are emitted in the exhaust gas, said components being combusted in the oxidizing catalytic converter thereby causing overheating of the converter.